1. Field of the Invention
The present invention relates to electrical connector assemblies, and more particularly to a connector assembly having two mating connectors used for high-speed signal transmission.
2. Description of the Prior Art
High-speed digital electronic apparatus, such as certain communication equipments and computer servers, require fast and accurate signal transmission. These apparatus have electronic components including connectors, wires, circuit boards, and integrated circuit packages. In low-speed applications, these components can function normally in cooperation with each other. However, in high-speed applications, conductivity and other electrical characteristics of these components become critical in ensuring that the electrical performance of the apparatus as a whole is satisfactory.
The faster the signal transmission required of an electronic apparatus, the harder it is to build suitable electrical connectors for the apparatus. One of the primary electrical factors affecting high-speed performance in connectors is cross talk mutually induced between two adjacent contacts of the connector. The intensity of cross talk depends on the distance between the two adjacent contacts.
Today, as electrical products become smaller and smaller, so too do their components such as connectors. In addition, the number of contacts in contemporary connectors is increasing due to the demand for more signal transmission paths and faster transmission speeds. Therefore, the distance between adjacent contacts inside a typical connector is becoming less and less. Cross talk induced between the contacts is becoming increasingly significant, and needs to be carefully addressed.
One way to deal with cross-talk inside a connector is to establish a ground reference means between every two contacts of the connector. U.S. Pat. No. 5,645,436 shows an example of a conventional connector system including jack and plug connectors. Each connector includes a plurality of signal contacts arranged in several rows and columns in an electrically insulative body. Signal paths comprising mutually engaged contacts of the jack and plug connectors have ground means alternately located therebetween. As a result, the number of contacts installed inside the jack and plug connectors is increased. In addition, manufacturing of the ground means and signal contacts becomes significantly complicated due to the different structural designs of the signal contacts and ground means. Furthermore, the increased number of contacts results in more difficulty when installing the contacts into the connector housing, because only a smaller pitch between every two adjacent receiving holes in the housing is available. These difficulties in manufacturing increase costs significantly, and do not necessarily guarantee better electrical performance.
Another way to deal with cross talk is to transmit differential signals in a connector, as described in the book High-Speed Digital Design (by Howard W. Johnson and Martin Graham, pp.319-320). Such connector can provide better electrical performance with regard to impedance matching, cross talk reduction, and electromagnetic interference (EMI) reduction. What is needed is an electrical connector transmitting differential signals, which can overcome the above-described shortcomings of conventional connectors.
It is therefore an object of the present invention to provide an electrical connector assembly for high-speed signal transmission which has a simplified structure and enhanced electrical performance.
To achieve the above object, an electrical connector assembly of the present invention is provided to electrically connect two printed circuit boards. The connector assembly includes a first board-to-board connector and a second board-to-board connector mounted on the two printed circuit boards respectively. The first connector comprises a first insulative housing receiving a multiplicity of first contacts. The second connector comprises a second insulative housing receiving a multiplicity of second contacts. The first housing comprises an insulative mating part, and a multiplicity of first contact-receiving passages defined therein. The first passages are arranged along two opposing lengthwise sides of the mating part, and receive the first contacts therein. The second housing defines a mating groove corresponding to the mating part of the first connector. The second contacts are positioned at two lengthwise sides of the mating slot, and correspond to complementarily mating first contacts of the first connector. Thus the first and second contacts can electrically mate with each other to electrically interconnect the two printed circuit boards.
In a first preferred embodiment of the invention, the first contacts comprise a plurality of first signal contacts, a plurality of first ground contacts, and a plurality of first shield-joint contacts.
The first contacts are arranged in the first passages, and divided into several successively arranged groups. In each group, there are two pairs of first signal contacts. Each pair of first signal contacts transmits one set of differential signals. Each pair of first signal contacts is installed in the first passages almost adjacent the other pair of first signal contacts, with one first shield-joint contact separating the two pairs of first signal contacts. A first passage between first signal contacts of the same pair is empty. Two first ground contacts are installed in two of the first passages at respective opposite ends of the group of first contacts.
The second contacts are arranged in the second passages corresponding to the respective first contacts. The second contacts comprise a plurality of second signal contacts, a plurality of second ground contacts, and a plurality of second shield-joint contacts. The second signal contacts are paired corresponding to the first signal contacts.
Due to the wide interval between adjacent signal contacts, cross-talk between adjacent signal contacts can be reduced. In addition, the signal contacts are well shielded by the ground contacts and the shield-joint contacts. This significantly facilitates suppression of any EMI noise emanating from these signal transmission paths. Furthermore, because the distances between the paired signal contacts is increased, the impedance of the first and second connectors increases at the same time in order to match impedance of the signal circuitry at other electronic components along the same signal transmitting paths.
In a second preferred embodiment of the invention, the empty passage within each pair of signal contacts is not present. A distance between adjacent passages receiving a pair of signal contacts is twice as long as a distance between any other adjacent passages. In a third preferred embodiment of the invention, a first passage between first signal contacts of the same pair has a spare contact that is not used to transmit any signals.
Other objects, advantages and novel features of the present invention will be drawn from the following detailed description of the preferred embodiments of the present invention with the attached drawings, in which: